The solar heat collection devices that use cylindrical-parabolic concentrators known in the state of the art are based on the developments arising from the construction of thermoelectric plants called “Segs”, which were implemented in the United States in the 1980s.
The known designs use structures that act as supports for the reflector elements that make up the parabolic reflector profile and the absorber tube located on the theoretical focal line of the parabolic cylinder formed by the reflectors. These structures are usually formed by inter-connected modules and equipped with an orientation mechanism that makes it possible to collect the maximum possible radiation by following the sun.
The reflector elements may be composed of different materials, made using different processes and supported in different ways, but, in any event, the objective is to obtain the maximum possible reflectivity and the maximum geometric precision such that, following the optical laws of reflection and refraction, the reflected beam interception deviation with respect to the theoretical focal point is as small as possible.
One of the main elements of the device is the tube in charge of absorbing the maximum possible energy of that reflected from the reflector surface and transmitting it as efficiently as possible to the heat-transfer fluid used. In order to prevent losses by thermal convection, the absorber tube, normally made of a metallic material with a suitable selective-layer coating, is surrounded by a glass envelope tube, and the intermediate space is subjected to high vacuum, which requires hermetic glass-metal joints and high-quality metal-metal welds subjected to vacuum. U.S. Pat. No. 6,705,311 describes specific solutions in this regard.
On the other hand, configuration of the device with completely airtight segments with high vacuum requirements has favoured the use of Getter systems for hydrogen absorption, such as that disclosed in US 2004134484.
The disadvantages of the solar collection devices known in the state of the art include the following:                High cost of the absorber tubes.        Breaking of the glass-metal joints, with the consequent loss of vacuum and, therefore, of yield.        Breaking of the glass tube at the joint areas.        Need to perform costly temperature and vacuum degasification processes that allow to activate the getter system.        Undetectability of the loss of vacuum in a tube or great uncertainty of the tracers specified, with low confidence regarding the information prior to the failure.        Possible saturation of H2 in the getter system through time for temperatures below the working temperature, which would cause a significant loss of yield.        Impossibility to easily measure the vacuum during the device's operating life.        Need to use materials such as glass for the envelope tube and glass-metal joints due to the high level of vacuum required.        High replacement cost in the event of breakage.        Impossibility to repair the replaced element.        Limited useful surface due to the need to absorb the differential dilations between the inner tube and the outer cover by means of bellows and connecting elements.        
This invention is intended to overcome these disadvantages.